Numerous teachings may be found in the prior art of causing gelatinization of a starch-containing material in the presence of water by employing steam for heating purposes. Generally, processes for heating the starch-containing material may be considered to be either batch or continuous type. Extrusion cooking may be regarded as one type of continuous gelatinization process while steam injection cooking may be seen as another type.
An example of a batch type process employing a tempered starchy material in a dry state is taught by Carey in U.S. Pat. No. 3,067,064, issued Dec. 4, 1962. The patentee discloses that a dry, free-flowing, starchy material is tempered in the presence of water at a temperature below the gelatinization temperature. Thereafter, a charge of this material is agitated in the presence of steam which brings about the necessary temperature increase to cause gelatinization. Heating times of 3 to 30 minutes are mentioned with optimum times of 5 to 10 minutes considered necessary to bring about the requisite degree of gelatinization.
Numerous patent teachings relate to continuous gelatinization in which it is necessary that the starch-containing material be employed in slurry form or as a high-moisture content feed. The former process is generally employed in steam injection cooking while the latter is frequently used in extrusion cooking. In the former process, steam is injected into the slurry and, in the presence of excess water at the elevated temperatures, the desired gelatinization takes place. Welch, U.S. Pat. No. 2,941,889, issued June 21, 1960, teaches a simple steam injection into a vegetable, such as corn, in the preparation of a cream-style product. Etheridge, U.S. Pat. No. 2,805,966, issued Sept. 10, 1957, and Winfrey et al, U.S. Pat. No. 3,133,836, issued May 19, 1964, both teach similar but different techniques of using a Venturi principle to obtain high turbulence while injecting steam into a slurry of a starch-containing material. Etheridge employs the principle of directly impacting steam radially or perpendicularly into a starch slurry stream on the order of a velocity of several thousand feet per second whereby extremely agitated and turbulent conditions are obtained. Winfrey et al also employ a Venturi principle, but the contact of the starch slurry and steam is essentially transverse to each other at controlled temperatures and a controlled excess of steam.
Another patent which teaches use of an eductor in gelatinization is Knoch, U.S. Pat. No. 3,374,096, issued Mar. 19, 1968. The process as described also requires an excess of water carrier for a starch slurry.
A batch type process, as exemplified by Carey, discussed above, has the advantage in that a slurry need not be employed and that dry granules may be utilized as the starting material. However, a batch type process has the disadvantage that requires extremely long cooking times with large capital investments for equipment when large quantities of the material are prepared.
A continuous type process of starch gelatinization has the advantage in that minimum amount of equipment is necessary and that fast flow rates may be employed. Conventional continuous processes, however, have the disadvantage in that the high moisture content of the gelatinized product prepared from slurries as in the case of a steam injection cooking process or from high-moisture content feed material as in the case of an extrusion cooking process eventually requires extensive drying operations.